Evolution

Summary

In biology, evolution is the change in heritable characteristics of biological populations over successive generations. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation. The theory of evolution by natural selection was conceived independently by Charles Darwin and Alfred Russel Wallace in the mid-19th century as an explanation for why organisms are adapted to their physical and biological environments. The theory was first set out in detail in Darwin's book On the Origin of Species. Evolution by natural selection is established by observable facts about living organisms: (1) more offspring are often produced than can possibly survive; (2) traits vary among individuals with respect

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https://en.wikipedia.org/wiki/Evolution

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Snow microstructure and its evolution play an important role for various applications of snow physics in cryospheric sciences. The main modes of microstructure evolution in snow are referred to as isothermal and temperature gradient metamorphism. The former describes the coarsening driven by interfacial energy while the latter is dominated by recrystallization processes induced by temperature gradients. An accurate description of these processes in snowpack models is of key importance. However common snowpack models are still based on traditional grain metrics, originally tailored to field observations, and empirical evolution laws. This treatment of snow microstructure is essentially unrelated to recent advances of snow observations by microcomputed tomography (ÎŒCT). The present thesis contributes to the solution of this problem by i) identifying suitable microstructure parameters ii) deriving evolution equations for these from first principles and iii) developing methods that allow to utilize 4D ÎŒCT measurements of snow as a link between local ice crystal growth and upscaled microstructure as relevant on the scales of interest for common snowpack models. To this end, three studies have been conducted. The first study focuses on estimating local ice-crystal growth rates from interface tracking by analyzing 4D ÎŒCT data of in-situ snow metamorphism experiments under isothermal and temperature gradient conditions. For temperature gradient metamorphism diffusion-limited growth is considered, while for isothermal metamorphism the data is compared to kinetics and diffusion limited growth. Despite considerable scatter, in both cases the significance of underlying growth laws could be statistically confirmed. The second study uses ÎŒCT images from a variety of snow samples to investigate the role of grain shape in the context of microwave and optical properties of snow. Grain shape can be objectively defined via size-dispersity of structure from the second moment of either the mean curvature distribution or the chord-length distribution. In addition, a quantitative link between these quantities and the exponential correlation length is shown. The latter is relevant for parameterizing macroscopic properties such as microwave scattering coefficients, dielectric permittivity and thermal conductivity. Finally, a rigorous, upscaled microstructure scheme is developed by deriving mathematically exact evolution equations for the density, specific surface area, the mean and Gaussian curvature and the second moment of mean curvature. The microstructural evolution is driven by local ice crystal growth. All parameters are upscaled by volume averaging and the correctness of the model is confirmed for the time evolution of idealized grains. The model can be compared to 4D ÎŒCT data without any a-priori assumptions. This benchmarking reveals the uncertainties of the interface tracking method which are largely caused by limited temporal and spatial resolution. The model allows to statistically assess the validity of ice crystal growth laws during snow metamorphism. For a temperature gradient experiment it is shown that a diffusion limited growth law is not consistent with the observed decay of the specific surface area. The developed model is a powerful and rigorous tool that is tailored to 4D ÎŒCT data. It connects microscale ice-crystal growth thermodynamics with the macroscale snowpack modeling.

EPFL2017

Property rights redistribution and the spatial evolution of the Chinese danwei compound: a case study in Beijing

Teng Zhang, Mengke Zhang

Danwei compounds were the dominant form of urban neighborhood in China's planned economy era. However, since the economic reform, the status of danwei compounds has undergone dramatic changes. By examining the transformation of Hua Gong Da Yuan (HGDY), a danwei compound in Beijing, this paper conceptualizes property rights redistribution and spatial evolution for post-danwei compounds. The transformation of danwei compounds is accompanied by the increasing awareness of property rights mainly in terms of land parcels, amenities and housing. Meanwhile, a more diversified group of property users, including both original residents and newcomers, are granted some portion of these property rights. They tend to privately claim all types of compound resources, which causes the spatial evolution of the compound, such as the reuse of former amenities, fragmented spaces and porous boundaries, the evolution of street shops, and the encroachment of public space. This paper argues that the institutional and proprietary order of post-danwei compounds is vaguely defined and disorderly arranged, which results in a weakened pattern of residual claims and compounds' deterioration. The study suggests an updated contract regarding danwei compounds to clearly regulate the behaviors of property users.

SPRINGER2021

Current and future spatial distribution of ticks (Ixodes ricinus) and of hosted Chlamydia in Switzerland

Morgan Bruhin

This project aims to study the spatial distribution of tick, I. ricinus, and emergent Chlamydiales families hosted by them. We used presence data associated with environmental variables to construct habitat suitability indexes by using species distribution modeling from the Maxent software. Most of the variables are climatic coming from the Worldclim website, also available for future climatic predictions. Additionally, the possible evolution of those habitats was estimated considering future climate conditions in 2070. We applied the previous species distribution modeling method with predictive variables to characterize their evolution. Finally, an estimation of the population exposed to this possible emergent threat to the human health under the form of a synthetic index. This index regroups the relative population density with the combination of the possible habitat of the tick and the hosted Chlamydiae. The results showed an expected general presence over the low altitude areas for the tick, but the predictive model failed to clearly identify areas of possible important modification of their suitable habitat. The Chlamydiae also admitted a possible habitat over most of the low altitude, mostly the Plateau. Their future evolution seemed to point out a homogenization of the distribution for those families over the Plateau.

2016

EPFL2017